While he was a graduate student in microbiology, Richard Blakemore was looking for Spirochaeta plicatilis in marine marsh mud when he first noticed something peculiar. After the sulfide rich mud had been stored on his shelves for a while, he noticed that the mud contained large amounts of bacteria moving across the microscope slide from south to north. This was a stark contrast to normal bacteria which move around randomly in no specific orientation. Blakemore wondered what was causing these bacteria to move in the manner that they did. There happen to be a window in the Northwest part of his lab and he first though maybe they were responding to the light. He disproved this theory when he observed that shining light on the bacteria from different directions made no difference in their movement. Then, Blakemore brought a magnet close to the bacteria on a microscope slide. He was astonished when he observed the bacteria immediately aligning themselves according to the magnetic field created by the magnet.
Upon further investigation under a transmission electron microscope, Blakemore discovered that each cell contained dense particles lined up in chains. These dense particles contained the iron mineral magnetite (Fe3O4). He also found that each crystal was enclosed in a membrane and is called a magnetosome. The crystals were arranged in long chain keeping the north/south orientation. It was originally thought that the magnetosomes allowed the bacteria to move according to the magnetic forces of the Earth. In such a case, they would move down toward the sediments that were oxygen poor. So, those bacteria that live in the Northern Hemisphere would swim toward the North Pole, while those that lived in the Southern Hemisphere would swim toward the South Pole. This type of movement is called magnetotaxis. However, recently researchers from MIT, the Woods Hole Oceanographic Institution (WHOI) and Iowa State University have found a bacterium in New England that does just the opposite in a Northern Hemisphere creature that swims south. Researchers now believe there must be other explanations for why some magnetotactic bacteria swim in particular directions.
Researchers are very interested in the magnetotactic bacteria for many reasons. One of these reasons includes the magnetotactic bacteria could serve as a possible model for the process of biomineralization and for its role in the evolution of the magnetotactic response in higher organisms. Also, magnetite has many commercial uses including magnetic tapes, magnetic targeting of pharmaceuticals, cell separation, and applications in magnetic resonance imaging.Magnetospirillum magnetotacticum is a very interesting and unique organism. The fact that it was discovered over 30 years ago and is still raising questions is amazing to me. Magnetotactic bacteria will continue to be studied for years to come and could lend a hand to understanding some biological mechanisms.
References
1). “Bacterium found to have strange magnetic character.” Massachusetts Institute of Technology. 17 Feb. 2006.11 March. 2006. http://web.mit.edu/newsoffice/2006/bacteria.html.
2). Clement, Sandi. “Magnetic Microbes.” 11 March. 2006. http://commtechlab.msu.edu/Sites/dlc-me/curious/caOc96SC.html
3). Faber, Cat. “Living Lodgestones: Magnetotactic Bacteria.” 2 July. 2001. 11 March 2006. http://www.strangehorizons.com/2001/20010702/living_lodestones.shtml.
4). Lory, Stephen., Perry, Jerome., and Staley, James. “Microbial Life.” Sunderland, MA: Sinauer Associates; 2002.
5). “Magnetospirillum magnetotacticum.” 11 March. 2006. http://genome.jgi-psf.org/draft_microbes/magma/magma.home.html.
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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